Switched-Mode Audio Amplifier Employing Power-Supply Audio- Modulation

Abstract

A device and method are disclosed for modulating a power converter based on an audio signal to directly drive a speaker with a differential audio output signal. A first modulation signal and a second modulation signal are generated based on an input audio signal so that the first and second modulation signals are complementary signals to each other. In one embodiment, a feedback signal, such as an acoustic feedback signal from the speaker, is also used to generate the first and second modulation signals. A power supply voltage is modulated with the first modulation signal to generate a first voltage signal. The power supply voltage is also modulated with the second modulation signal to generate a second voltage signal. The first and second voltage signals form a differential audio signal that is used to drive the speaker. Alternatively, the power converter can drive a speaker with a single-ended output signal.

What is claimed is: 
     
         1 . An audio amplifier, comprising:
 a modulator to receive an audio input signal and to output a first modulation signal corresponding to the audio input signal; and   a first regulator coupled to a power supply and the first modulation signal, the first regulator to generate a first voltage signal from the power supply that is modulated by the first modulation signal, the first voltage signal corresponding to the audio input signal.   
     
     
         2 . The audio amplifier according to  claim 1 , wherein the modulator is to further output a second modulation signal corresponding to the audio input signal, the first and second modulation signals being complementary to each other;
 the audio amplifier further comprising:   a second regulator coupled to the power supply and the second modulation signal, the second regulator to generate a second voltage signal from the power supply that is modulated by the second modulation signal, the second voltage signal corresponding to the audio input signal, and the first voltage signal and the second voltage signal forming a differential audio signal based on the complementary first and second modulation signals.   
     
     
         3 . The audio amplifier according to  claim 2 , wherein the first regulator and the second regulator each comprise Class D amplifiers; and
 wherein the first regulator and the second regulator both comprise boost regulators, or buck regulators, or single-ended primary-inductor converter (SEPIC) regulators.   
     
     
         4 . The audio amplifier according to  claim 3 , further comprising a microphone to generate an acoustic feedback signal of a speaker coupled to the differential audio signal formed by the first and second boosted voltage signal, and
 wherein the modulator is further to receive the acoustic feedback signal and to further output the first and second modulation signals corresponding to the audio input signal and the acoustic feedback circuit.   
     
     
         5 . The audio amplifier according to  claim 4 , further comprising a first feedback signal corresponding to the first voltage signal and a second feedback signal corresponding to the second voltage signal,
 wherein the modulator is further to receive the first and second feedback signals and to further output the first and second modulation signals corresponding to the audio input signal, the acoustic feedback circuit, and the first and second feedback signals.   
     
     
         6 . The audio amplifier according to  claim 3 , further comprising a first feedback signal corresponding to the first voltage signal and a second feedback signal corresponding to the second voltage signal,
 wherein the modulator is further to receive the first and second feedback signals and to further output the first and second modulation signals corresponding to the audio input signal and the first and second feedback signals.   
     
     
         7 . The audio amplifier according to  claim 2 , wherein the first and second modulation signals comprise pulse-width modulated (PWM) signals or pulse-density modulated (PDM) signals. 
     
     
         8 . The audio amplifier according to  claim 2 , wherein the first regulator comprises a first boost regulator comprising:
 a first inductor comprising a first terminal and a second terminal, the first terminal of the first inductor being coupled to the power supply;   a first switching device comprising a first terminal, a second terminal and a third terminal, the first terminal of the first switching device being coupled to a return path to the power supply, the second terminal of the first switching device being coupled to the first modulation signal, and the third terminal of the first switching device being coupled to the second terminal of the first inductor;   a first active pass device comprising a first terminal, a second terminal and a third terminal, the first terminal of the first active pass device being coupled to the third terminal of the first switching device and the second terminal of the first inductor, the second terminal of the first active pass device being coupled to first modulation signal, and the third terminal of the first active pass device being coupled to an output of the first boost regulator, the output of the first regulator outputting the first voltage signal; and   wherein the second boost regulator comprises a second boost regulator comprising:   a second inductor comprising a first terminal and a second terminal, the first terminal of the second inductor being coupled to the power supply;   a second switching device comprising a first terminal, a second terminal and a third terminal, the first terminal of the second switching device being coupled to the return path to the power supply, the second terminal of the second switching device being coupled to the second modulation signal, and the third terminal of the second switching device being coupled to the second terminal of the second inductor;   a second active pass device comprising a first terminal, a second terminal and a third terminal, the first terminal of the second active pass device being coupled to the third terminal of the second switching device and the second terminal of the second inductor, the second terminal of the second active pass device being coupled to second modulation signal, and the third terminal of the second active pass device being coupled to an output of the second regulator, the output of the second boost regulator outputting the second voltage signal.   
     
     
         9 . An amplifier, comprising:
 a modulator to receive an audio input signal and at least one feedback signal and to output a first and second modulation signals corresponding to the audio input signal and the at least one feedback signal, the first and second drive modulation signals being complementary to each other;   a first power converter coupled to a power supply voltage and the first modulation signal, the first power converter to generate a first voltage signal from the power supply voltage that is modulated by the first modulation signal; and   a second power converter coupled to the power supply voltage and the second modulation signal, the second power converter to generate a second voltage signal from the power supply voltage that is modulated by the second modulation signal, the first and second voltage signals forming a differential audio output signal.   
     
     
         10 . The amplifier according to  claim 9 , wherein the first power converter and the second power converter comprise Class D amplifiers; and
 wherein the first power converter and the second power converter both comprise boost regulators, or buck regulators, or single-ended primary-inductor converter (SEPIC) regulators.   
     
     
         11 . The amplifier according to  claim 10 , wherein the at least one feedback signal comprises an acoustic feedback signal of a speaker coupled to the differential audio output signal. 
     
     
         12 . The amplifier according to  claim 11 , wherein the at least one feedback signal further comprises a first feedback signal corresponding to the first voltage signal and a second feedback signal corresponding to the second voltage signal. 
     
     
         13 . The amplifier according to  claim 10 , wherein the at least one feedback signal further comprises a first feedback signal corresponding to the first voltage signal and a second feedback signal corresponding to the second voltage signal. 
     
     
         14 . The amplifier according to  claim 9 , wherein the first and second modulation signals comprise pulse-width modulated (PWM) signals or pulse-density modulated (PDM) signals. 
     
     
         15 . The amplifier according to  claim 9 , wherein the first power converter comprises a first stepped-up power converter comprising:
 a first inductor comprising a first terminal and a second terminal, the first terminal of the first inductor being coupled to the power supply voltage;   a first switching device comprising a first terminal, a second terminal and a third terminal, the first terminal of the first switching device being coupled to a power supply return path, the second terminal of the first switching device being coupled to the first modulation signal, and the third terminal of the first switching device being coupled to the second terminal of the first inductor;   a first active pass device comprising a first terminal, a second terminal and a third terminal, the first terminal of the first active pass device being coupled to the third terminal of the first switching device and the second terminal of the first inductor, the second terminal of the first active pass device being coupled to first modulation signal, and the third terminal of the first active pass device being coupled to an output of the first power converter, the output of the first stepped-up power converter outputting the first voltage signal; and   wherein the second power converter comprises a second stepped-up power converter comprising:   a second inductor comprising a first terminal and a second terminal, the first terminal of the second inductor being coupled to the power supply voltage;   a second switching device comprising a first terminal, a second terminal and a third terminal, the first terminal of the second switching device being coupled to the power supply return path, the second terminal of the second switching device being coupled to the second modulation signal, and the third terminal of the second switching device being coupled to the second terminal of the second inductor;   a second active pass device comprising a first terminal, a second terminal and a third terminal, the first terminal of the second active pass device being coupled to the third terminal of the second switching device and the second terminal of the second inductor, the second terminal of the second active pass device being coupled to second modulation signal, and the third terminal of the second active pass device being coupled to an output of the second power converter, the output of the second stepped-up power converter outputting the second voltage signal.   
     
     
         16 . A method, comprising:
 generating a first modulation signal and a second modulation signal based on an input audio signal, the first and second modulation signals being complementary to each other;   modulating a power supply voltage with the first modulation signal to generate a first voltage signal; and   modulating the power supply voltage with the second modulation signal to generate a second voltage signal, the second voltage signal and the first voltage signal forming a differential audio signal based on the complementary first and second modulation signals.   
     
     
         17 . The method according to  claim 16 , wherein generating the first and second modulation signals comprises generating the first and second modulation signals based on the input audio signal and at least one feedback signal. 
     
     
         18 . The method according to  claim 17 , wherein the at least one feedback signal comprises an acoustic feedback signal of a speaker coupled to the differential audio signal. 
     
     
         19 . The method according to  claim 17 , wherein the at least one feedback signal comprises a first feedback signal corresponding to the first voltage signal and a second feedback signal corresponding to the second voltage signal. 
     
     
         20 . The method according to  claim 16 , wherein the first and second modulation signals comprise a pulse-width modulated (PWM) signals or a pulse-density modulated (PDM) signals.